1. Field of the Invention
The present invention relates to a gyro for detecting the rotation angular velocity, more particularly, to a tuning fork type vibration gyro utilizing 1 piezoelectric element.
2. Description of the Related Art
Gyroscope have been used as means for identifying the position of moving objects such as airplanes, large vessels, space satellites, and the like. Recently, they have been utilized for detecting vibration of apparatus such as car navigation, VTR, still cameras, and the like in civil use.
Among such gyroscopes, a vibration gyro made by utilizing a piezoelectric element has been in practical use. The piezoelectric vibration gyro is made by utilizing the principle that, when a rotation angular velocity is exerted upon an object which is vibrating at a predetermined rate, Coriolis force is formed in a direction orthogonal to the direction of vibration. Various types of such piezoelectric vibration gyros have been proposed. Above all, recently, research and development of a tuning fork type vibration gyro utilizing the piezoelectric monocrystal such as LiTaO.sub.3, LiNbO.sub.3, etc., have been vigorously pursued.
The tuning fork type vibration gyro has a constitution comprising two arms formed in one-piece in a piezoelectric monocrystal and a base supporting the two arms, and having a constitution comprising a drive electrode provided on the arm for driving the tuning fork vibration and a detection electrode provided on the arm for detecting the rotation angular velocity. This tuning fork type vibration gyro is classified into the following two types according to the installation pattern of the drive electrode and detection electrode. One type is that a drive electrode is provided on one arm and a detection electrode on the other arm (hereinafter, this type is called asymmetric type). The other type is that both a drive electrode and a detection electrode are provided on the respective arms, and the electrode installations in both arms are symmetric (hereinafter, this type is called a symmetric type).
This tuning fork type vibration gyro is advantageous in the points of small size, light weight, and low cost in comparison with other gyros of coma gyro, optical gyro, etc., but is inferior to other gyros in respect to measuring precision. Therefore, improvement of measuring precision, i.e., improvement of S/N ratio, is desired in the tuning fork type vibration gyro.
In the asymmetric type tuning fork type vibration gyro referred to above, the drive electrode and the detection electrode are provided respectively on the separate arms. For this reason, abnormal vibration is generated and a potential difference as noise caused thereby is detected. Another problematic point is unnecessary output (leaking output) attributed to the mechanical coupling and electrostatic coupling between the arm provided with a drive electrode and the arm provided with a detection electrode. On the other hand, in the symmetric type tuning fork type vibration gyro referred to above, such abnormal vibration can be prevented, and leaking output is also small, but there are problems such that the capacity ratio is high and the detection sensitivity is small.